A convention's Guest of Honor (often abbreviated "GoH" from Guest of Honor) is the title given to people the convention is specifically honoring. The GoH is normally a pro of some sort (a Fan Guest of Honor being an equal but different title), but "Guest of Honor" is also frequently used as a generic term applying to all kinds of guest including both pros and fans.

A person is usually made a GoH to recognize significant and long-lasting contributions to the SF field or the SF community. (Of course, conventions hope that having a famous name at their convention will draw more attendees, also.) Because of this, repeating GoHs is uncommon and generally frowned on.

Worldcon GoH
The ultimate GoHship is, of course, being GoH at Worldcon — it's fandom's equivalent of a Nobel Prize. There is a sensible and long-standing rule of thumb that a Worldcon GoH should have at least thirty years activity in the field before being honored. (The thirty year number is arbitrary, but has proven to be about right — there are always many potential deserving guests with at least that length of activity — and does an excellent job of discouraging the honoring of one-hit wonders and charismatic flash-in-the-pans.)

A Worldcon GoH is a member of the community whose contributions have had a substantial (positive!) impact on the community. A GoH should be one of the people who made us what we are. (See Fan GoH for more on this.)

The oldest Worldcon tradition was to have a single GoH. A second, a FGoH, was added in the 50s and the number of GoHs at a typical convention has gradually increased. More than about five (even at a Worldcon) is considered crass, though, sadly, some conventions go much further, greatly diminishing the honor. (As a rule, Guests of Honor are individuals, but sometimes a couple will be honored and occasionally a group (e.g., The Stranger Club at Noreascon Three). Those cases are generally counted as a single guest, albeit one with multiple heads.)

Another common practice is to reserve "Guest of Honor" for a pro writer and have other specific GoHships such as Fan Guest of Honor, Artist Guest, Filk Guest, etc. If so, this does not normally indicate a difference in ranking. Everyone called a "guest of honor" of any flavor is equal.

Special GuestsSpecial Guests are sometimes Guests of Honor and sometimes not — this is a convention-dependent thing. (For Worldcons, Special Guest is never a GoH unless specifically designated as such.) A good way to judge if an ambiguously designated person is a real GoH or simply an important person whose presence is being noted is to count the other guests. If there's reasonably full slate of GoHs without the ambiguous cases, they are probably not GoHs.

Other "Guests"
In general, a "guest" at an SF convention is one of a small number of people whose expenses (but never an appearance fee or honorarium) are paid by the con. When the word "guest" is used to describe someone formally, it practically never refers to the general run of program participants. None-the-less, many conventions use the term "guest" loosely, especially in publications, to mean all program participants.

There are also working positions like toastmaster and program participants which are sometimes headlined in publicity and called "guests" of the convention, but they are not Guests of Honor.

Commercial and media conventions do not follow these rules and frequently have either no GoHs or a plethora of them. While many of the practices were adopted from fandom's, they are not longer part of the community and are not further considered here.

Common GoH Designations

just-plain-GoH

Can mean a generic (unspecified type) GoH and is also commonly used to refer to the pro writer GoH. It depends on local custom.

A broader category than filk. A Music GoH can be a filker or someone from the mundane music scene. (Hopefully with a ties tot he sf community and not just entertainment.)

Gaming

Science

Special

A very confusing category. Sometimes it effectively means "Other GoH" or "GoH-but-we-don't-have-a-neat-category" and sometimes it means "Not a GoH per se but someone we wish to honor or note." Sometimes used to advertise the expected presence of a potential draw. It depends strongly on local custom. See Special Guest for more.